A sliding fire door has previously been disclosed in the specifications of Japanese Patent Laid-Open No. 9858/1980 and Japanese Utility Model Publication No. 107577/1980 wherein opening of the door is accomplished by a manual operation, and closing is automatically effected with an adjustable force which varies the returning speed provided by an elastic device in order to vary the time of closing of the sliding fire door. In this door, a self-closing action begins the instant that a restraint is released by the action of a smoke sensor or a heat sensor. A suspension door provided with a self-closing function only is disclosed in the specification of Japanese Patent Laid-Open No. 123236/1979; and a sliding fire door is disclosed in the specification of Japanese Patent Laid-Open No. 138692/1984 wherein a smoke-shielding plate is perpendicularly provided toward a ceiling.
The above-described sliding fire door and suspension door, however, provide insufficient security in terms of protecting people from a fire, because they are incapable of preventing an outflow of harmful smoke when they are closed and this leads to a problem in that such doors are unsuitable for many purposes.
The aforementioned sliding fire door is unsuitable in practice since harmful smoke leaks out from a space formed between both ends of the door or in the vicinity of a suspension wheel.